The accident occurred in the very heart of an unruly cloverleaf known as the MacArthur Maze, where several major arteries converge at the approach to the Bay Bridge, which connects San Francisco with the cities and suburbs that line the east side of San Francisco Bay.

The California Highway Patrol identified the driver of the tanker as James Mosqueda, 51, from Woodland, Calif., near Sacramento. Officer Trent Cross, a spokesman for the highway patrol, said Mr. Mosqueda had just picked up the gasoline from a nearby refinery and was headed to a gas station near the Oakland airport when the accident occurred.

The highway patrol believes that Mr. Mosqueda was heading south on an interchange of Interstate 80 when he lost control in a curve, hit a guardrail and flipped his truck on its side. The tanker exploded, sending flames hundreds of feet into the air, according to witnesses, and quickly buckled a three-lane section of Interstate 580 and caused it to collapse onto Interstate 880 some thirty feet below.

Michael Brown, the commissioner of the highway patrol, said the driver was able to escape the burning truck and apparently hailed a cab in order to go to the hospital. Mr. Brown said there was “no indication of impairment of the driver” by drugs or alcohol, but that some legal issues are outstanding for both Mr. Mosqueda, and the truck’s owner, Sabek Transportation, based in San Francisco.

Photo

A fiery pre-dawn tanker truck accident caused the collapse of heavily used freeway overpass near downtown Oakland early this morning.Credit
Peter DaSilva for The New York Times

For some Bay Area residents, the accident evoked memories of the 1989 Loma Prieta earthquake, which caused the collapse of a mile-long, double-decker section of I- 880, near the site of today’s accident. That collapse, which occurred during the evening rush hour, resulted in 41 deaths and more than 100 injuries, as cars on the lower level were crushed. Mayor Gavin Newsom of San Francisco, who visited the site today, called the collapse “a giant wake-up call to the region” about what might happen in a major temblor.

“It’s a matter of when not if,” Mr. Newsom said.

This time around, the results were not deadly on I-880, but no less arresting to look at. Dozens of people converged near the collapse site to gawk at the damage, and rubbernecking drivers on remaining roadways slowed traffic.

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“I was on the road last night, so it’s kind of scary for me,” Anita Myles, 49, an Oakland resident, said as peered at the damage through a chain link fence.

Another onlooker, James Signore, a civil engineer from Oakland, said he had a professional interest in the damage. “I have not seen this kind of wreckage before,” said Mr. Signore, 43. “And I’m really curious how something this stout could be taken down.”

He was not the only one wondering how the overpass, which dates to the 1950’s, had failed. At a noontime press conference held at a toll plaza near the collapse, Mr. Kempton said the heat from the fireball had likely melted the steel girders and bolts that support the concrete roadway. “If you have that kind of heat, you’re going to have this kind of reaction,” he said. “We’re not surprised this happened.”

With a Monday morning rush hour looming, officials said they were trying to assess the damage as fast as possible. Even with fewer cars on the road on a sunny weekend afternoon, traffic was slow coming off the Bay Bridge into the East Bay, a situation that will no doubt intensify as the work week begins. On an average day, the two spans that were destroyed this morning carry 160,000 vehicles, Mr. Kempton said.

Bay Area Rapid Transit, the train system connecting San Francisco and the East Bay, was not affected by the accident. Additional trains were being added and existing trains lengthened to accommodate more passengers.

“We would encourage people to stay away from maze,” Mr. Kempton said. “If experience tells us anything, it will take a day or two to get this sorted out.”

That may be a very rosy assessment. Rebuilding the collapsed section of I-880 took nearly a decade, though Mr. Kempton called that situation “a much larger issue” involving neighborhood and environmental concerns. Mr. Kempton said he had contacted Gov. Arnold Schwarzenegger’s office soon after the accident, and would seek federal highway funds for repairs, something he estimated would cost tens of millions of dollars. “It’s not going to be cheap,” he said.

He also pleaded for patience, saying with this kind of complex highway system, “You’re not going to have a picnic every day.”